1. Field of the Invention
The present invention relates to concrete casting equipment and accessories and, more particularly, to a composite core body for the positioning of an anchor element in a prefabricated concrete member in such a way that an exposed end portion of the anchor element is positioned within an arcuate recess of the concrete member.
2. Description of the Prior Art
It is known to utilize recessed "lost anchors" for the handling of heavy prefabricated concrete members. The recessed arrangement of the anchor elements has the advantage of eliminating the need for a cutting operation on the anchor element, after the concrete member has been hoisted to its intended place in the building structure.
A hoisting attachment which features such a recessed anchor element is disclosed in U.S. Pat. No. 3,883,170. The hoisting harness includes a torus-shaped clasp-like hoisting shackle with a transverse slot and an arcuate locking bolt reaching across the slot and cooperating with an exposed eye portion of the anchor member engaged in the slot. The result is a secure connection which can be released by retracting the arcuate locking bolt of the shackle behind its transverse slot.
This hoisting attachment features an oblong arcuate recess in the concrete member to enable the torus-shaped hoisting shackle to reach over and engage the anchor element whose eye portion is arranged in the center of the recess. The casting of such a recess and the positioning of the anchor element are accomplished with the aid of a special core body which has the shape of a flattened spheroid which has been cut in half transversely. This core body encloses and holds the later exposed eye portion of the anchor element while being attached to the inside of a side plank of the formwork.
It has been found that, in order to safely attach the anchor element in a cantilever-type connection with the core body, the flanks of the core body engaging the eye portion of the anchor element must also engage the eye opening itself. This presents a problem in connection with the removal of the core body from the finished concrete member in that the release of the core body from the anchor element necessitates an opening movement on the part of these anchor positioning flanks. This problem is solved by arranging the anchor positioning flanks in the core body as opposite sides of a transverse groove which reduces the mid-portion of the core body to a thin bridge portion. This bridge portion forms a flexible hinge between two quarter-sectors of the "flattened spheroid", for the required opening displacement of the anchor positioning flanks.
The prior art suggests for the core body to be made of natural rubber or vulcanized rubber. For its attachment to the formwork, it includes at least one embedded nut which is engageable by a bolt or threaded rod. Frequently, at least one of the two anchor positioning flanks is formed by an embedded steel insert, in order to improve the cantilever-type connection for the anchor element. This steel insert includes a protrusion which fits into the eye opening of the anchor element. The opposing flank is a flat rubber face. Obviously, the use of a steel insert makes the core body more complex and therefore more expensive.
A major shortcoming of a core body of rubber is its tendency to develop brittleness as a result of aging of the rubber, especially in those portions of the core body in which it is repeatedly compressed or flexed.